Optical non-destructive evaluation (NDE) has been used in numerous materials characterization applications in the aerospace, semiconductor, and other industries. Conventional optical NDE methods are based on speckle interferometry, speckle photography, or double-exposure holography. Such speckle-based methods take advantage of the speckle patterns produced by the scattering of monochromatic light, such as a laser light flux, from a rough surface and do not require physical contact with a specimen to assess specimen properties.
Speckle-interferometry and double-exposure holographic methods tend to be unsuited to measurement of many specimens of interest. In addition, such conventional methods frequently do not provide sufficient measurement resolution. While some optical NDE methods have been used to evaluate industrial specimens, these methods are generally impractical in typical engineering and manufacturing environments. For example, strain measurements of circuits and circuit components are especially difficult. Accordingly, improved measurement methods and apparatus are needed.